linux-kernel - Re: [syzbot] [block?] BUG: unable to handle kernel NULL pointer dereference in lo_rw

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Message-ID: <680ae64e.050a0220.317436.0052.GAE@google.com>
Date: Thu, 24 Apr 2025 18:33:02 -0700
From: syzbot <syzbot+6af973a3b8dfd2faefdc@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, lizhi.xu@...driver.com, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [block?] BUG: unable to handle kernel NULL pointer
 dereference in lo_rw_aio

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: unable to handle kernel NULL pointer dereference in filemap_read_folio

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 0 P4D 0 
Oops: Oops: 0010 [#1] SMP KASAN NOPTI
CPU: 2 UID: 0 PID: 46 Comm: kworker/u32:2 Not tainted 6.15.0-rc3-syzkaller-g02ddfb981de8-dirty #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: loop8 loop_rootcg_workfn
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc90000a3f5a0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff81f2b3ae
RDX: ffff88801f2bc880 RSI: ffffea0000e2d740 RDI: ffff88801fc48e00
RBP: ffffea0000e2d740 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000002be0 R12: 1ffff92000147eb5
R13: ffff88801fc48e00 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8880d6bb2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000012f76000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 filemap_read_folio+0xc5/0x2a0 mm/filemap.c:2401
 filemap_create_folio mm/filemap.c:2536 [inline]
 filemap_get_pages+0xf39/0x1c20 mm/filemap.c:2597
 filemap_read+0x3d2/0xe90 mm/filemap.c:2702
 generic_file_read_iter+0x344/0x450 mm/filemap.c:2894
 lo_rw_aio.isra.0+0x9c2/0xd90 drivers/block/loop.c:393
 do_req_filebacked drivers/block/loop.c:424 [inline]
 loop_handle_cmd drivers/block/loop.c:1866 [inline]
 loop_process_work+0x8a4/0x10d0 drivers/block/loop.c:1901
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3319 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
CR2: 0000000000000000
---[ end trace 0000000000000000 ]---
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc90000a3f5a0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff81f2b3ae
RDX: ffff88801f2bc880 RSI: ffffea0000e2d740 RDI: ffff88801fc48e00
RBP: ffffea0000e2d740 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000002be0 R12: 1ffff92000147eb5
R13: ffff88801fc48e00 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8880d6bb2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000012f76000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


Tested on:

commit:         02ddfb98 Merge tag 'scsi-fixes' of git://git.kernel.or..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16aefd9b980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=efa83f9a6dd67d67
dashboard link: https://syzkaller.appspot.com/bug?extid=6af973a3b8dfd2faefdc
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=110efd9b980000